As a vehicle accrues mileage, the catalytic converter deteriorates. The deterioration results in a less effective catalyst. To monitor catalytic converter deterioration, the fuel injection system uses two heated oxygen sensors: one which is upstream of the catalytic converter and one downstream of the converter.
The PCM compares the reading from the sensors to calculate the catalytic converter oxygen storage capacity and storage efficiency. The PCM also uses the upstream heated oxygen sensor input when adjusting the injector pulse width. When the catalytic converter efficiency drops below preset emission criteria, the PCM stores a Diagnostic Trouble Code (DTC) and illuminates the Malfunction Indicator Lamp (MIL).
The automatic shutdown relay supplies battery voltage to both of the heated oxygen sensors. The sensors have heating elements which reduce the amount of time it takes for the sensors to reach operating temperature.
- Visually check the connector, making sure it is properly attached, and that all of the terminals are straight, tight and free of corrosion.
- Allow the heated oxygen sensor to cool to room temperature.
Use an ohmmeter to test the heating element of the heated oxygen sensors:
- Detach the electrical connector from each oxygen sensor. The white wires in the sensor connector are the power and ground circuits for the heater elements.
- Connect the ohmmeter test leads to the terminals of the white wires in the heated oxygen sensor connector.
- Replace the heated oxygen sensor if the resistance is not 5-7 ohms for 1995 vehicles or 4-7 ohms for 1996-98 vehicles.
Before installing a new oxygen sensor, perform a visual inspection. Black, sooty deposits on the sensor tip may indicate a rich air/fuel mixture. White, gritty deposits could result from an internal antifreeze leak. Brown deposits indicate oil consumption. All of these contaminants can damage a new sensor.
REMOVAL & INSTALLATION
See Figures 1 and 2
- Disconnect the negative battery cable. On Cirrus, Stratus, Sebring convertible and Breeze models, disconnect the negative battery cable at the remote location on the left strut tower.
- Raise and safely support the vehicle.
- Unplug the upstream oxygen sensor connector.
- If removing the downstream oxygen sensor, detach the sensor electrical harness from the clips along the body.
- Remove the sensor using a suitable oxygen sensor crow's foot wrench. After removing the sensor, the exhaust manifold must be cleaned with an 18mm x 1.5 + 6E tap.
- New oxygen sensors will be packaged with a special anti-seize compound already applied to the threads. If you are reinstalling the old sensor, the sensor threads must be coated with fresh anti-seize compound. You must use the correct type of anti-seize compound containing liquid graphite and glass beads. This is not a conventional anti-seize paste; the graphite will tend to burn away, but the glass beads will remain. The use of a regular compound may electrically insulate the sensor, rendering it inoperative. You must coat the threads with an electrically conductive anti-seize compound.
- Carefully thread the sensor into the bore, then tighten to 20 ft. lbs. (28 Nm) on Cirrus, Stratus, Sebring convertible and Breeze models, or 33 ft. lbs. (44 Nm) on Sebring and Avenger coupes.
- If installing the downstream oxygen sensor, route the sensor electrical harness through the clips along the body.
- Attach the oxygen sensor electrical connector.
- Carefully lower the vehicle, then connect the negative battery cable.